نشریه صوت و ارتعاش
پیاپی 20 (پاییز و زمستان 1400)

The first part of this paper discusses the importance of porous materials in passive noise reduction, types of porous materials, various applications of these materials, relevant acoustical and non-acoustical parameters, and different methods to measure them based on international standards were explained. In this part of the paper, definitions and experimental methods used in measuring the acoustic properties of the absorption coefficient and the sound transmission loss based on international standards are presented. Then, while providing a comprehensive discussion of the sound absorption mechanisms in porous materials, the types of sound absorption mechanisms, including viscous, thermal, and structural losses, are described. The effect of different parameters on the variation of sound absorption of porous materials has been presented. Also, various models, including experimental, laboratory, and analytical models used for expressing the acoustical and mechanical properties of porous materials, are discussed. Finally, a brief review is present for recent research areas on porous materials.

Denim washing is an artistic payment process that aims to increase the attractiveness and strength of denim fabrics. Much of the world's textile industry is devoted to the production of denim. Jeans are the most widely used clothing in the clothing business. Because of the mechanical properties of ultrasound, it accelerates and replaces particles. In this study, the simultaneous effect of ultrasonic waves, enzymes, and sodium hydrosulfite were investigated to increase the production rate. Evaluation of the results of Denim washing samples was performed with a Projectina microscope and scanning of samples. The results of eye observation of the samples and their weight evaluation confirmed the effectiveness of ultrasonic waves. But in Iran, less of this technology is used in textile design. Therefore in this study, the application of ultrasonic in the designing of jeans has been discussed.

Ultrasonic welding as a new technology in many industries has replaced the usual methods of joining such as welding, brazing, sewing and etc. In this technology, ultrasonic energy is generated by the ultrasonic transducer and transmitted to the joining area through the booster and horn. Ultrasonic energy is dissipated and absorbed in the joining area and generates heat. Simultaneous application of static force / pressure and heat causes the involved parts to join with each other. In this process, various parameters such as power, frequency, static force / pressure, time, material and shape of parts and etc affect the joining properties and the resulting sample. In this paper, with the aim of acquainting researchers with the principles and applications of this technology, scientific and industrial research in the field of ultrasonic welding has been reviewed. Due to the major application and different effective mechanisms, this paper is divided into two main parts of metal welding and plastic welding. Considering the importance and application of the subject, the principles and methods of applying ultrasonic vibrations, different mechanisms of ultrasonic, the parameters of the ultrasonic welding process and the important applications of this technology have been studied. Finally, a perspective on the application of high power ultrasonic vibrations in new manufacturing and joining technologies in the future of the industry is presented.

Immersed boundary method is a novel and efficient tool for solving fluid-structure interaction problems. One of important fluid-structure interaction problems is vortex-induced vibrations of cylinders. In this study, we want to introduce immersed boundary method. Philosophy, advantages, disadvantages and applications of the method will be presented. Because of wide range of applications of this method and for not losing focus, we shall limit our study only to vortex-induced vibrations. Next, details of governing equations of immersed boundary method and their discretization will be introduced. Iterative immersed boundary algorithm which has been used for vortex-induced vibrations before, will be used to solve governing equations. Finally, implementation and coding requirements will be discussed. This paper is organized in a way so readers can obtain a comprehensive understanding of the method behavior in fluid-structure interaction problems, especially vortex-induced vibrations. Considering the benefits of immersed boundary method, it has the potential to become the main method for analyzing fluid-structure interaction problems. These benefits are considerable enough that makes the implementation of the method justifiable.

Usually, in dynamic analysis of mechanical systems, joints are supposed to be ideal and complete and effects like clearance, local deformations, wear and lubrication are ignored. These types of boundary conditions have small deviations from the ideal conditions and named as non-ideal boundary conditions. In this research the effect of non-ideal boundary conditions on the free vibrations of a Euler-Bernoulli simply supported beam, as a weakly nonlinear system, has been analyzed and investigated. For this purpose, the boundary conditions in clearance supports are assumed to be non-ideal and the equations of vibration of the beam are analyzed by both Lindstedt-Poincaree and multiple scales perturbation techniques and results are compared. It was observed that the results of the two methods are compatible with together. In order to validate the methods, by assuming the perturbation parameter to be zero, the frequency obtained from the two methods is compared with the frequency of the previous references, which have equal results. To investigate the issue, one of the boundary conditions supposed to be non-ideal, In this case the existence of clearance increases the amplitude of the mode shape but depending on the number of mode, can lead to increasing or decreasing natural frequencies. Also, the existence of clearance in a support causes the asymmetry of the shape of modes.

Sound is one of the important factors in creating the desired feeling in a mosque and can be used as a sensory inductor to establish a spiritual relationship with God. On the other hand, several architectural factors affect the acoustic quality and therefore sound can be considered as a link between architecture and mosque performance. In order to evaluate the acoustic conditions of the mosque, the present study has measured the two standing and sitting positions in order to simulate the prayer positions. form and volume are the two considered architectural parameters and Background Noise, Reverberation Time and Sound Pressure Level are the three acoustic variables studied and 15 historical mosques of Tabriz have been tested in 4 volumetric and 5 formal categories. The study was cited in ISO 3382 and the measurements were performed with B&K equipment and Acoustic Camera. The results show that the formal classification of the study does not have much effect on the acoustic status and the main differences are due to volume changes. This proves the existence of a specific sound ID for historical mosques in Tabriz, which originates from the executive form of materials. Samples have common structural elements such as arches, protruding walls, corners, decorations such as ‘karbani’, column surface, etc. with the same materials that cause similar acoustic feedback by sound propagation.

Wheel squeal noise is one of main annoying noise through railways that it is occurred when train passing tight curves. Different noise reduction methods are applied for this problem, but each one has limitations. In this paper, a hybrid method is proposed that comprises an active dithering control on rail using piezoelectric stack actuators and increasing wheel modal damping by attaching shunted piezoelectric patches on it. An experimentally validated transient wheel squeal noise is used for investigation proposed method. The model includes linear dynamics of railway track and wheel-set and nonlinear contact forces. The dithering control on rail, applying high frequency and low amplitude signal, is designed for wheel squeal noise suppression on low frequencies. The shunt circle is resonant type that can be adjusted on specific frequency and causes maximum damping. The modal damping on two modes is increased by dividing attached piezoelectric patches on two group with dedicated shunt circles. The results show proposed method significantly reduce sound pressure level of wheel squeal noise on all frequency domain.

Nowadays, the use of ultrasound in the food industry is very important and its widespread application as a non-thermal process in heat-sensitive foods has attracted increasing attention, due to the preservation of sensory, nutritional and functional properties along with increasing shelf life and creating safety against microbial activities. The application of ultrasound in processes such as emulsification, distribution and dispersion, dissolution, and stabilization has been made possible and accelerated. The processes that play a significant role in the preparation and manufacture of films and coatings for use in the packaging industry. In other words, one of the most important applications of ultrasound is its use in the manufacture and design of various packaging materials, including natural or biodegradable packaging materials, and nano-packaging materials. Because the distribution and uniformity of the particles in the polymer matrix is very important and in fact all the expected properties of a packaging film depend on this uniformity and distribution. The use of ultrasound helps to this the film to be even and evenly distributed. In addition, since ultrasound is now used as a process aid alongside other processes for decongesting, decontamination, extraction, extrusion, extraction, wastewater treatment, etc .; this paper discusses the application of ultrasound in the food industry especially the production of food packaging films. Furthermore, the importance of the physical properties of the ultrasound device used in scientific studies is mentioned in this article.

Continuous/long-term monitoring of ocean temperatures and currents is important to better understanding of ocean dynamics as well as to study the effect of global warming on the oceans. Acoustic Tomography (AT) is one of the most effective techniques for monitoring the oceans. The AT technique calculates the flow characteristics based on the travel time law of the acoustic waves and computes the difference in the time of arrival of the acoustic signals at different stations. Oceanic AT instruments measure the temperature and currents in the scale of tens of thousands of kilometers by transmitting acoustic waves of less than 1 kHz. In this research, firstly, the theoretical fundamentals of the AT technique are discussed, then, the important researches are investigated. Due to the technology transferring of AT systems to Iran, applying this technique in the northern Indian Ocean and the Strait of Hormuz will provide valuable information to the researchers and decision-makers.

Composite materials are increasingly employed in varying industries. Health monitoring in composite members is a further issue of interest to researchers. When damaged, the structure responds differently because of alterations in mechanical properties (i.e., mass, stiffness, and damping). The health of the structure and structure members can be monitored by examining how the responses have changed. This paper aimed to detect damage in an 8-layer composite plate, in which each pair of successive layers are connected at a 90-degree angle. First, the composite plate was modeled and undergone frequency analysis in ABAQUS software and the information concerning damaged and non-damaged modes was extracted. Subsequently, the damage was detected by defining a two-dimensional signal (the sum or difference of the shape of healthy and damaged modes) as the input of a two-dimensional discrete wavelet transform. The results showed turbulence and perturbation in the wavelet coefficients obtained from the diagonal details of the input signal’s wavelet analysis in damaged areas so that with a simple inspection, the damaged areas could be easily identified. According to the results, the proposed technique is an efficient method of damage detection in laminated composite plates.

Today, ultrasound technology has found a special place in medical surgery. In recent years, researchers have tried to upgrade this technology to perform various surgeries. The most important features of ultrasound surgical equipment compared to traditional models are accurate cutting and no damage to surrounding tissues, less bleeding, reduced tissue healing time, Easier operation of the surgeon and, also the possibility of affecting some tissues in a non-invasive way. Due to the importance and many applications of this issue, this article examines the applications of ultrasound technology in medical surgery, the parameters affecting the equipment used in this field and, the mechanisms of the effect of ultrasound in the body. In addition, ways to advance this technology in medical surgery, challenges and, the future of scientific and industrial research in this field are also presented. challenges and, the future of scientific and industrial research in this field are also presented.

Today, lobed mixers are recognized as an effective means in reducing noise in turbofan engines. In this study, the effect of mixing hot and cold flow in a lobed mixer on noise reduction is surveyed and simulated. Navier Stokes equations are considered to be three-dimensional, compressible, unsteady, and turbulence. The k-ω SST equation has been used to solve the turbulent flow, and the Ffowcs Williams Hawkings (FW-H) model has been used to investigate the sound pressure level. The results of this study show that the amount of sound pressure level(SPL) decreases as the output current moves away from the nozzle. Also, the frequency range between 80 and 10,000 Hz is considered. At 80 Hz, there is the highest sound pressure level, and as the frequency increases, the sound pressure level decreases. The results show that the sound pressure level at frequencies below 1000 Hz is higher than other frequency ranges.